Skip to main content

Subphylum Cephalochordata (Branchiostoma): General Characters, Classifications and Affinities | B.Sc. II Year Zoology

In this article, we will discuss the characters, classifications(Subphylum: Cephalochordata)  and affinities of Branchiostoma.

Characters of Branchiostoma:

General Characters of Branchiostoma:

1. Marine, widely distributed in shallow waters.

2. Mostly sedentary and buried with only anterior body end, projecting above bottom sand.

3. Body small, 5 to 8 cm long, slender, fish-like, segmented and transparent.

4. Body has trunk and tail. Head lacking.

5. Paired appendages lacking. Median fins present.

6. Exoskeleton absent. Epidermis single-layered.

7. Muscles dorso-lateral, segmented into myotomes.

8. Coelom enterocoelous, reduced in the pharyngeal region by development of atrial cavity.

9. Notochord rod-like, persistent, extending from rostrum to tail, hence, the name Cephalochordata.

10. Digestive tract complete. Pharynx large, perforated by numerous persistent gill-slits opening into atrium.

11. Respiration through general body surface. Special organs for respiration absent.

12. Circulatory system well developed, closed without heart and respiratory pigment. Hepatic portal system developed.

13. Excretion by protonephridia with solenocytes.

14. Nerve cord dorsal, tubular without ganglia and brain. Dorsal and ventral nerve roots separate.

15. Sexes separate. About 25 pairs of gonads. Gonoducts lacking. No asexual reproduction.

16. Fertilisation external in sea water.

17. Development indirect, including a free-swimming larva.

18. Cephalochordata has about 30 species of the genus Branchiostoma and all put in the class Leptocardii.

Classifications Of Subphylum: Cephalochordata



Primitive, Degenerate and Specialised Characters of Branchiostoma (Cephalochordata):

Primitive Characters:

Primitive characters are relics from its original ancestors. They are those characters which are developed and perfected in the course of evolution and they generally show progress.

Primitive characters of Branchiostoma are as follows:

1. There is no specialised head.

2. Absence of paired limbs or fins.

3. The epidermis is made of a single row of cells and a true dermis is absent.

4. Coelom enterocoelous.

5. A complete notochord is persistent throughout life with no vertebral column.

6. There is a complete metameric segmentation of myotomes from one end to the other, as in the embryo of vertebrates, and this obvious metamerism is retained throughout life.

7. Alimentary canal is a straight tube without loops, and the midgut diverticulum is a hollow tube. Jaws absent.

8. A peculiar pharynx specialised for ciliary feeding in which sorting of food takes place after a food-laden current of water enters the pharynx, this involves taking a very large volume of water and its continuous removal through numerous gill-clefts.




Comments

Post a Comment

Popular posts from this blog

Classification of Subphylum Cephalochordata (Amphioxus)

In this article we will discuss about the classification of subphylum Cephalochordata. Historical Resume of Subphylum Cephalochordata : The first individual of this group was des­cribed by Pallas in 1778. He regarded the speci­men as a slug and named it Umax lanceolatus. Yarrell (1836) studied the animal in detail and gave the name Amphioxus lanceolatus. Costa (1834) suggested the name of the genus as Branchiostoma. Since then the biological name of the genus has been established as Branchiostoma according to the law of priority. Important Features of the Subphylum Cephalochordata Lankester, 1877 : [Gk. Kephale, a head], Approx. 23 species. a. Cephalochordates are small, fish-like translucent marine chordates. b. The body is laterally compressed and tapered at both ends with a post-anal tail. They are commonly called “lancelets” for the shape of the body. c. There is a low continuous dorsal and cau­dal fin; no paired fins. d. Body muscles are arranged as a series of V-shaped blocks of ...
1 comment
Read more

Herdamania: Structure, Locomotion and Systematic Position

In this article we will discuss Herdmania:-  1. Habit and Habitat of Herdamania  2. External Structures of Herdamania  3. Body Wall  4. Coelom and Atrium  5. Locomotion  6. Digestive and Respiratory Systems  7. Circulatory System 8. Excretory System  9. Nervous System  10. Reproductive System  11. Affinities and Systematic Position of Herdmania  Contents:  1. Habit and Habitat of Herdamania: Herdmania is a solitary Aascidian. It is exclusively marine. The genus is recorded to go to the depth of 9 m – 21.6 m of the sea. The adult is a sessile form which remains attached to the substratum by its base or foot. It is a microphagous animal which feeds on micro-scopic animals and plants. The tunic of Herdmania provides shelter for many organisms. A very common occur¬rence is the growth of a green alga on the tunic which sometimes hides the whole animal. The other organisms inhabiting the tunic are the hydroids, anemones, minutes lam...
Post a Comment
Read more

Pila Globosa: Habitat, Sense Organs and Development

  In this article we will discuss about Pila   Globosa:- 1.  Habit and Habitat of Pila Globosa 2.  External Features of Pila Globosa  3. Coelom 4. Digestive System 5. Respiratory Organs 6. Blood Vascular System 7. Excretory System 8. Nervous System 9. Sense Organs 10. Reproductive System 11. Copulation 12. Fertilisation 13. Development. Contents: Habit and Habitat of Pila Globosa External Features of Pila Globosa Coelom of Pila Globosa Digestive System of Pila Globosa Respiratory Organs of Pila Globosa Blood Vascular System of Pila Globosa Excretory System of Pila Globosa Nervous System of Pila Globosa Sense Organs of Pila Globosa Reproductive System of Pila Globosa Copulation of Pila Globosa Fertilisation of Pila Globosa Development of Pila Globosa 1. Habit and Habitat of Pila Globosa : Pila globosa or the apple snail is one of the largest freshwater molluscs. It is commonly found in freshwater ponds, pools, tanks, lakes, marshes, rice fields and sometimes even...
Post a Comment
Read more